1. Field of Invention
This invention relates to the prevention of accidental needle-stick injuries wherein health care workers (HCW) become infected with blood-borne pathogens, such as human immuno-deficiency viruses (HIV), hepatitis B viruses (HBV, hepatitis C viruses (HCV), herpes simplex viruses (HSV), Epstein-Barr viruses (EBV), etc.; and wherein patients become infected by such pathogens carried in the blood of an infected HCW, or a HCW accidentlly needle stuck during use of a syringe for injecting the contents of a fluid-filled cartridge.
2. Description of the Prior Art
The use of cartridge-loaded syrettes to inject the contents of cartridges containing fluid medications, especially penicillin, morphine or cocaine derivatives, through cartridges with permanently attached needles has been common medical practice since World War II. There are two kinds of such cartridge-loaded syrettes in common use: side-loading and breech-loading. A breech-loading syrette customarily has a cartridge receiving chamber in the trailing end of its barrel for in-loading cartridges with permanently attached needles, and a hinged metal breech-block containing a sliding plunger for expelling fluid from the cartridge. The barrel has a large-bore aperture on the leading end which securely holds the expanded hub of a leading needle by means of matching threads. (See U.S. Pat. No. 2,778,359 issued Jan. 22, 1957 to Friedman). The most commonly used models are metallic "Tubex" brand syrettes made by Wyeth. Plastic side-loading models, such as Wyeth Tubex Fast-Trak Syringe, quick-loading; and Wyeth-Ayerst Tubex Injector (U.S. Pat. No. 4,642,103 issued Jan. 7, 1986 to Gettig) are now available. However, the former is not suited to easy and safe disposal of the cartridge with an attached needle; while the latter projects an unprotected glass or plastic cartridge/needle into chosen sites customarily outside of the mouth. Because the cartridge is usually made of glass, and the leading end attached to the needle is fragile, such unitized cartridges are not suited for dental use.
The fundamental features of such reusable medical syrettes are to allow single injections of pre-measured quantities of fluid or semi-fluid medications with minimal opportunity for contamination of such fluids or the injecting needle before or during the course of injection into a patient. However, there are hazards inherent for the user, owing to possible needle-stick injury prior to safe disposal of the spent unitized cartridge/needle. These hazards are addressed through provision of attachable two part scabbards for standard metallic and plastic syrettes and syringes. Since 1950 a modified syrette, commonly known as the "Carpule Aspirator" has become the standard means for giving dental anesthesia in the U.S. and in other nations. The "Carpule Aspirator" has advantages over the "Tubex" syringe in that the trailing end of the syringe plunger is supplied with a thumb-ring which allows the user to aspirate or inject with one hand, while feeling for anatomical land-marks with the other. For the dental user, the "Carpule Aspirator" has other advantages in that the plunger inside the carpule is activated by an arrow-head which pierces and holds the plunger and, thus, is quicker to attach than a threaded mechanism on the trailing end of the inside plunger. Because injections for insuring adequate dental anesthesia are often into several different sites, and often require one or more reloading of carpules, this would seem advantageous. However, the "Carpule Aspirator" syringe has disadvantages, because the carpules which load through the side are not supplied with permanently attached needles. Therefore, the leading end of the "Carpule Aspirator" barrel is threaded to receive a double-ended needle which is manually screwed on and detached at the leading end of the syrette. The assembly is easy and inexpensive to use, but provides needle-stick hazards for the dental client, as well as the dentist and co-workers which are outlined in the MMWR: Recommended Infection-Control Practices for Dentistry Apr. 18, 1986 Vol. 35/#15:237-242 whose relevant portions read as follows:
1. Sharp items (needles, scalpel blades, and other sharp instruments) should be considered as potentially infective and must be handled with extrordinary care to prevent unintentional injuries.
2. Disposable syringes and needles, scalpel blades, and other sharp items must be placed into puncture-resistant containers located as close as practical to the area in which they were used. To prevent needlestick injuries, disposable needles should not be recapped; purposefully bent or broken; removed from disposable syringes; or otherwise manipulated by hand after use.
3. Recapping of a needle increases the risk of unintentional needlestick injury. There is no evidence to suggest that reusable aspirating-type syringes used in dentistry should be handled differently from other syringes. Needles of these devices should not be recapped, bent, or broken before disposal.
4. Because certain dental procedures on an individual patient may require multiple injections of anesthetic or other medications from a single syringe, it would be more prudent to place the unsheathed needle into a "sterile field" between injections rather than to recap the needle between injections. A new (sterile) syringe and a fresh solution should be used for each patient.
In order to arm such a "Carpule Aspirator"syringe with the double-ended needle used for draining carpules and injecting anesthetic, the user must use two hands to screw on said double-ended needle to cap the leading end of said syringe. Between injections with the same needle to empty one or more carpules, the leading tip of said double-ended needle must not be recapped using two hands, and is better left in a sterile field which might not be easy to maintain. After final use, the leading tip of said double-ended needle must be recapped using two hands in order to uncap the leading end of said syringe before said double-ended needle can be disposed safely into a sharps container. In short: dentists should not needle-cup syrettes or re-cap double ended needles.
Recognizing the hazards of attaching double-end needles to dental syrettes, in U.S. Pat. No. 4,334,536 issued Jun. 15, 1982, Pfeger described pre-filled syringes in which the means for attaching the needle assembly to the syringe, the needle cover and the activating mechanism are unitized, but breakable at specific points to expose the needle and empty the syringe. However, Pfeger provided no means for safely protecting the needle after use. In U.S. Pat. No. 4,767,413 issued Aug. 30, 1988, Haber et al described a disposable dental syrette which manually retracts and safely re-sheaths the needle back into the syrette after the cartridge contents have been injected. Such syrettes are considered to be user-safe with respect to needle stick injuries, but can not be re-used and, hence, expensive. In U.S. Pat. No. 5,007,901 issued Apr. 16, 1991 a method is described for safely retracting a detachable needle used for insertion of an intravenous catheter into a disposable syringe to protect the patient and the user during and after use, but this assembly is not suitable for dentists, especially for giving single injections into multiple sites.
The barrels and muzzles of reusable medical and dental syringes or syrettes are not customarily supplied with any kind of scabbard; and are normally autoclaved before reuse. However, disposable medical luer-lock syringes with detachable needles, such as "Monoject" brand produced by Sherwood Medical Corporation are customarily encased in capped puncture-resistant plastic scabbards which keep the syringes and pre-attached needles sterile before use; and which can be reused to recap the needle, as well as the entire syringe after use. Such scabbards can be used to safely dispose of the used needles and syringes into sharps containers, but the fitting of parts, relative diameters and mode of operation differ from those described here. In brief, the "Monoject" system uses the hub of the injection needle as the focal point for the interplay of frictional forces during a two-handed recapping of the needle; whereas the co-pending invention uses the leading tip of a syringe as a large focal point to hold the leading portion of the armed syringe by impaction in a puncture resistant scabbard until ejected by manual control or gravity into a convenient sharps container.
In addition, Sherwood Medical produces a disposable "418" dental injector with a reusable plastic holder, similar to the Wyeth Tubex Injector (U.S. Pat. No. 4,642,103), to securely hold the trailing end of the injector which, in turn, is made to empty a 1.8 ml. standard carpule by means of a plunger with a customary arrow-head configuration and a double-ended needle permanently attached to the leading end of the injector. After the carpule is emptied via the double-ended needle, the injector is replaced into the puncture-resistant scabbard wherein it was originally packaged; the reusable plastic holder is manually detached; and, then, the disposable holder and carpule are disposed into a sharps container. With respect to needle-stick injuries, this "418" assembly is theoretically much safer than the standard metal "Carpule Aspirator" syringes to which double-ended needles must be bi-manually attached and detached by means of threads. However, the "418" is difficult to manipulate during attachment and detachment of the plastic holder; during reinsertion of the needle and trailing injector into the original scabbard; and during manipulation of the plunger, especially when the arrow-head becomes mis-aligned.
During the last three years, major manufacturers of luer-lock syringes have manufactured sliding plastic scabbards permanently attached to standard disposable luer-lock syringes. After use of the syringe/needle in a patient, the plastic scabbard is advanced over the barrel of the syringe, usually using two hands, such that the leading open end of the scabbard extends beyond the tip of the needle and, then, maintained there by a locking mechanism between the barrel of the syringe and the scabbard which slides over. The disadvantages of such assemblies are that they are not easy to use with one hand, the locking mechanism between syringe and over-riding scabbard is complex, the cost is 1.5 to 2 times as much as that of the original disposable luer-lock syringe lacking a permanently-attached sliding scabbard, and are not easily adapted to dental use or reuse for giving more than one injection.
The addition of a circular external flange to the trailing end of a pre-loaded unitized cartridge/needle intended for injecting dental anesthetics or solutions under sterile conditions by means of a reusable syringe with an activating plunger is novel, at least in the current practice of administering dental anesthesia. Alexandre in U.S. Pat. No. 4,944,677 (JUL. 31, 1990) describes a flange which connects a dental mandrel to the motor and a mandrel for fabricating of such apparatus from a conventional disposable dental needle. Dragan in U.S. Pat. No. 5,061,179 (Oct. 29, 1991) describes a flange which locks the trailing end of a cartridge to the trailing chamber in a manually operated dental extruder for viscous material so that the cartridge can not become detached or become wedged between flexible side walls.
A gap in the circular flange for fitting a projection in the chamber of a dental syringe, such that the cartridge can not rotate and the bevel of the needle is maintained in a constant position with respect to a dental syrette, is also novel. However, in the Monoject "418" dental injector, two flanges are placed near the trailing end of the injector to provide attachments for a reusable plastic holder. Such flanges are placed near, but not at the trailing end of the injector; and do not resemble the circular flanges which form the trailing end or "rim" of a rifle or shot gun cartridge.
Similarly, a corresponding modification of the trailing end of the chamber of a breech-loading reusable dental syrette to receive the circular flange and hold the slot in fixed position, appears novel. Therefore, it is cogent to described mechanical modifications in syrettes which will help users to employ such integrated modifications efficiently at minimal cost to patients.